.box {
  display: flex;
  .small {
    position: relative;
    width: 300px;
    height: 225px;
    cursor: move;
    .small-img {
      display: block;
    }
    .mark {
      position: absolute;
      width: 100px;
      height: 100px;
      background-color: rgba(0, 0, 0, 0.3);
      top: 0;
      left: 0;
    }
  }
  .big {
    margin-left: 20px;
    width: 300px;
    height: 300px;
    overflow: hidden;
    position: relative;
    .big-img {
      position: absolute;
      top: 0;
      left: 0;
      display: block;
    }
  }
}
